When a piece of bone protrudes from the knee joint, the first thing to distinguish is whether there is really a piece of bone, or some other condition. If it is a real piece of bone protruding, there may be several conditions: 1, bony free body, will suddenly appear, belong to the free state, sometimes missing; 2, chronic appearance, may be a bone disease, called osteoma; 3, osteophytes; 4, muscle atrophy around the knee joint will find the bone a little protruding, muscle atrophy for many reasons, common is lumbar spine disease or stroke sequelae; 5, tendons Chronic inflammation at the point of attachment can appear to be a little prominent, and in this case there is often pressure pain.